Generally, electrographic toners have been prepared by compounding a polymer resin, a colorant such as a pigment or dye, and other additives, if desired, on a heated roll mill to thoroughly mix the materials. After cooling the resulting mixture is ground into fine particles to obtain usable toner. Another method that has been suggested is to dissolve the polymer resin in a solvent, mix in the colorant and other desired additives, and spray dry the resultant solvent mixture to obtain usable toner particles. In each of these methods for manufacturing toner, the resin is first polymerized, then colorant and other additives are mixed with the polymer, and finally the mixture is treated to produce fine particles of solid toner for use. It has been suggested that by combining the colorant and additives with monomers prior to or during the polymerization of the resin, usable toner particles could be prepared as the end product of the polymerization and further processing steps eliminated.
A particularly useful electrographic toner comprises a resin having a high styrene content and carbon black as a pigment. Therefore, it is desirable to polymerize styrene monomers in the presence of carbon black to produce styrene containing electrographic toners without additional processing steps.
In this regard, British Pat. No. 1,237,095 published June 30, 1971, describes a process in which styrene and n-butyl methacrylate are emulsion polymerized in the presence of carbon black. The resulting polymerized emulsion is then spray dried to obtain toner particles of usable size for electrography.
It is desirable to make polymers containing high quantities of styrene moiety, i.e., 40 weight percent and greater, by suspension polymerization in the presence of untreated carbon because the suspension polymerization beads can be made of appropriate size for useful electrographic toner particles and no additional treatment (such as spray drying as in British Pat. No. 1,237,095) is necessary. The polymerization of olefins, including styrene, in the presence of surface-treated carbon blacks is described in U.S. Pat. Nos. 3,166,541; 3,179,648; 3,202,644; 3,216,990; and 3,221,002. The surface treatment of carbon blacks is expensive and/or treated carbon blacks can require special handling techniques. Therefore, it would be desirable to have a process for suspension polymerizing a styrene-containing monomer composition to produce polymers having more than 40 weight percent styrene moiety in the presence of untreated carbon.
U.S. Pat. No. 3,634,251 issued Jan. 11, 1972, describes a process for the suspension polymerization of a monomer having a polar radical selected from --NH.sub.2, --OH, --NO.sub.2 or halogen in water in the presence of coloring material and an insoluble inorganic fine powder such as calcium hydroxide, calcium carbonate, barrium hydroxide, barrium carbonate, zinc oxide, aluminum oxide, etc., which acts as a dispersion stabilizer. Example 1 of U.S. Pat. No. 3,634,251 describes the polymerization of 20 weight percent p-aminostyrene and 80 weight percent styrene in the presence of carbon black. No mention is made of surface treatment for the carbon black. However, since I have found that aminostyrene and styrene do not polymerize in the presence of untreated carbon black (see examples later in this specification), it must be presumed that treated carbon black was used. Example 2 of U.S. Pat. No. 3,634,251 describes the suspension polymerization of 8 weight percent p-nitrostyrene, 2 weight percent p-chlorostyrene and 90 weight percent styrene in the presence of Spilon Black, a metalized oil-soluble dye. Thus, to my knowledge, no one has described a process for suspension polymerizing a styrene-containing monomer composition in the presence of untreated carbon black to produce polymers having greater than 40 weight percent styrene moiety.